GB2276049A - Intruder deterrent lamp-control device - Google Patents

Description

2276049 DETERRENT DEVICE This invention relates to a deterrent device and

in particular, it relates to a deterrent device for use in a house or building to automatically switch lights on and off to give that house or building the appearance of being occupied.

Such deterrent devices are sometimes known as "intelligent lights". Various models are available, they comprise an adaptor one end of which provides a plug which fits in a light bulb socket: the other end of the adaptor provides a socket which is adapted to receive a light bulb. Such adaptors include means to measure light levels in the vicinity of the socket and an electric circuit which may, depending on the model selected, include a microprocessor, which when the deterrent device is activated determines whether the light bulb is switched on or off. Such deterrent devices as described above (hereinafter referred to as "deterrent devices of the type described") are often activated by quickly switching the light on, off, and on at the mains. The light bulb will then stay off until the light level drops at dusk andthe microprocessor and/or electric circuit in the adaptor is arranged to switch the light bulb on and then depending on the model selected either leave the light bulb switched m until dawn,, or switch the light m and off for part or all of the night according to a pre-set routine. When the adaptor/light is switched off at the mains the adaptor ceases to function and the light is used by switching it m at the mains as a normal light.

One problem with existing deterrent devices is that they are predictable and tend to switch the light on and off at the same times and for the same periods every night they are activated. Thus, by watching the house for a few nights, a would-be house burglar would be able to learn the pattern of light switching of the deterrent device, and would then be able to tell whether or not the deterrent device was activated or not and hence whether the householder was "in,, on a particular night or whether he was,out,,, by observing the pattern of light switching on that night.

A second problem with such deterrent devices is that they tend to be rather bulky, particularly the devices which include microprocessors and which are arranged to switch a light on and off at various times during the night, because the circuit for controlling the switching on and off of the light bulb includes a large number of bulky components. The problem arises in part because mains voltage at 240 volts AC has to be reduced to low voltage DC in order to run the microprocessor, which in turn has to supply a current of the order of 10-15 mA, to a relay, triac or other switching device operating the light bulb and to avoid the problem of heat generation a bulky "power capacitor', is used to drop the voltage. Further, if product liability insurance is required for the deterrent device an even larger and more expensive power capacitor which has underwriters, laboratories approval must be used.

Finally, if a householder goes out having activated a deterrent device of the type described, and returns home to find the light off, he does not know whether the deterrent device is still activated and the light has been switched off by the microprocessor or whether the house has been burgled and the burglarhas switched the adaptor and light off at the mains. If the house has been burgled the burglar might still be present in the house.

Aspects of the present invention are directed to alleviating various of the above-mentioned disadvantages of existing deterrent devices.

According to a first aspect of the present invention there is provided a deterrent device. comprising an adaptor including a plug means which is connectable to a light bulb socket and a socket means which is arranged to be able to receive a light bulb wherein the adaptor includes means for switching the light bulb on and off said means including a triac connectable in series with the light bulb across an AC mains electricity supply, the gate of the triac being controlled by the microprocessor and wherein in use current is supplied to the gate of the triac for a short period after each zero crossing of the AC c = ent through the triac, the arrangement being such that the average c = ent supplied to the gate of the triac to drive the triac is less than would be required if the triac were driven continuously.

The advantage of this first aspect of the present invention is that the microprocessor needs to draw less c = ent, to drive the triac since although the same value of c = ent drawn to drive the triac (10-15 mA) is needed, it need only be drawn for a fraction of the mains cycle. For example, at SOHz there are 100 zero crossings per second so if 10-15 mA is supplied to the gate for 0.2 ms after each zero crossing then that current is supplied for only 0.02s every second, so the average current is reduced by a factor of fifty. Hence the average current drawn is less, and in turn the microprocessor draws significantly less power from the mains and enables the use of resistors to reduce the mains voltage from 240 volts AC to 5 volts DC as opposed to the power capacitor which was needed in previous deterrent devices of the type described. This enables the deterrent device of the present invention to be made much smaller.

6 In a preferred embodiment, the microprocessor includes a clock which is arranged to time the period between the time when the deterrent device is switched on, off and on at the mains and if that time is less than a certain short period to switch the deterrent device into its activated mode.

In a second aspect of the present invention, there is provided a deterrent device of the type described wherein the microprocessor is arranged to switch the light bulb on and off at random.

In the presently preferred embodiment, the microprocessor includes an internal counter which is is switched on when the device is activated and which counts until after the light sensing means determines it is dusk. At a particular time after dusk the values of one or more of the bits of the random number generated by the counter at dusk is used to determine how long the light bulb is switched on for. The counter continues to run and when the light is switched off the number on the counter is used to generate the duration the light bulb is off for.

According to a third aspect of the present invention there is provided a deterrent device of thetype described which when activated is arranged to switch a light bulb on around dusk and then continue to switch the light bulb on and off during a first period wherein on average, the light bulb is on for 70-95% of the duration of the first period and off for 5-30% of that period, followed by a second period during which the light is on for 5-30% of the duration of that period and off for 70-95% of the period on average.

Preferably, the light is on for 85-95%,, and off for 5-15%, of the first period and off for 85-95%, and on for 5-15% of the second period.

Conveniently the first period may be between 4 to 8 hours long: the second period may be 2 to 4 hours long.

In a fourth aspect of the present invention there is provided a deterrent device of the type described which includes infra red or radio receiving means arranged to switch the light bulb on when a suitable 8 signal is received. Alternatively the device may be sound activated.

A specific embodiment of the invention will now be described by way of example only and with reference to the accompanying drawing which is a circuit diagram for a deterrent device embodying the present invention.

The deterrent device is of the type described in the introduction; the housing, plugs and sockets included in the device are well known to the skilled man and are not described.

The differences between the embodiment of the present invention and existing deterrent devices lie in the controlling circuit 100 of the device which is shown in figure 1, which shows a lamp 101, which is screwed into the adaptor and is controlled (i.e. switched on and off) by a triac 102, which is itself controlled by c = ent flowing from a microprocessor 104 to its gate 102A, via a resistor 106. The microprocessor 104 is supplied by approximately 5 volts DC across capacitor 108 after the mains 240 volts AC has been dropped across a series of three resistors 110, 112, 114, with a diode 116, Xener diode 118 and capacitor 108 smoothing and rectifying the current to produce DC.

The circuit also includes a further resistors 122, 124, 126, 128, 130, 132, 134 and 136, transistor 138 and a light dependent resistor 140. Further components - resistors 142 and 144 diode 146 and capacitor 148 provide an external timing network whose function will be explained later. The circuit includes provision at 134 indicated by "TYPE SELECT" for the connection of links into the circuit. The microprocessor is progra so that these connections determine the "type,, of deterrent device. The types are 3 hour, 6 hour, 9 hour, "all night" or dusk to dawn: this has advantages in the manufacturing process since only one progran microprocessor is needed to enable the manufacture of five different types of deterrent devices reducing stocks of microprocessor components required and making manufacturing more flexible. The three hour type of deterrent device remains active for three hours after dusk; the six hour, six hours after dusk; the nine hour, nine hours after dusk; and the all night remains active until dawn. The "dusk to dawn" embodiment merely switches the light bulb ON at dusk and switches it OFF at dawn.

All the components of the circuit including the microprocessor 104 are surface mounted and thustake up very little space apart from the triac 102.

The operation and features of the adaptor will be described in general terms before specific functions are addressed. The microprocessor 104, controls the operation of the device. When the deterrent device is in its activated state it is progran to switch the lamp 101 ON at dusk. The microprocessor determines is when it is dusk by measuring the resistance of the light dependent resistor 140 and is arranged so that "dusk" occures when the light level surrounding the adaptor falls below 3/6 lux. The microprocessor then switches the lamp 101 ON and OFF via a triac 102, the pattern and duration of light switching being determined, inter alia,, by the microprocessor and the links of the TYPE SELECT.

Specific functions of the circuit will now be explained with reference to the components of the circuit and programmes run by the microprocessor.

As can be seen from figure 1, triac 102 controls lamp 101. If the triac is switched on itconducts electricity between its terminals 102B and 102C and the lamp 101 is ON. The state of the triac (ON or OFF) is controlled by the c = ent flowing into its gate 102A and the current passing through the triac (i.e.

between 102B and C). Unless a c = ent of 10 to 15 mA is supplied to gate 102A the triac will be switched OFF every time the modulus of the current passing through it falls to zero. As the triac is connected across the mains at 50 Hz the current is zero 100 times every second. However instead of driving the triac with 10 to 15 mA continuously to keep the lamp 101 lit, the microprocessor 104 is arranged to supply between 10 and 15 mA to the triac to switch it on and for a short period (0. 2 ms) immediately after the c = ent through the triac falls to zero.

The fact that the gate of the triac is only supplied by 10-15 mA for 200 microseconds, 100 times per second means that the power supplied to the triac to operate the lamp is a tiny fraction (a fiftieth) of that which would be needed if the triac was driven continuously and this enables a much lower c = ent to be taken from the mains by the microprocessor which in turn enables resistors to be used to reduce the mains voltage to 5 volts instead of a power capacitor, because the average c = ent through the resistors is very law and very little heat is thus generated in them. If 10-15 mA were used to drive the triacs continuously the c = ent passing through the resistors would cause them to heat up.

The microprocessor includes a clock which counts zero crossings of the AC mains electricity via resistors 112r 114, 122 and 124 and, as is well known in the art, timing is based on the mains electricity being supplied at 50 Hz.

A second important feature of the embodiment of the present' invention is the randomness of the light switching operation. As has been described above, the lamp 101 is controlled by the c = ent supplied to the triac 102, when current is supplied to gate of the triac as described above the lamp is ON. When no c = ent is supplied to the gate of the triac the lamp is OFF. In controlling the supply of c = ent to the gate of the triac, the microprocessor thus controls the lamp.

The microprocessor includes an internal counter which counts to 256 in binary (i.e. an eight bit number) every 100 microseconds. The counter switches on and starts counting when the deterrent device is activated. When the value of the 1DR 140 corresponds to "dusk,' the clock in the microprocessor counts for is three minutes and then takes a second reading from the 1DR 140 to check that it is in fact dusk. A reading is then taken from the counter. This provides an eight bit random binary number (between 0 and 256 in denary) since it depends on the time when the deterrent device was activated which is clearly variable and the actual time "dusk" falls which is a variable which depends on the weather, the time of year, and other factors. To the last five bits of the random number, 6 is added, and since' the bottom five bits can equal any integer - 14 between 0 and 31 inclusive in denary this givesa random integer "All having a value between 6 and 37 inclusive. The device then switches the light ON for W' minutes. At the end of that time a second reading is taken from the counter. The number 1 is added to the last two bits of the number and since a two bits binary number can be either 0, 1, 2 or 3 in denary notation this gives a random number "B" which is either 1, 2, 3 or 4. The device switches the light OFF for "B" minutes. At the end of that time a further reading is taken from the counter to generate a number between 6 and 37 as before and the device continues in the like manner switching the light bulb ON and OFF periodically.

is The first period of light 'W' is clearly random within the constraints that it is between 6 and 37 minutes.

Further because, the counter counts so fast relative to the clock small variations in temperature, AC mains frequency, etc mean that even after the first ON period is chosen, that does not determine the future periods as small deviations are greatly magnified in the number generation system used. This effect is increased because the lowest value digitsof the counter are used to generate the ON and OFF periods.

If the device is a three or six hour device, the light will switch ON for between 6 and 37 minutes, switch OFF for between 1 and 4 minutes then switch ON for between 6 and 37 minutes and continue in like manner before switching OFF at the end of the three or six hour period respectively. If the device is a nine hour or "all night" device, it will switch ON for between 6 and 37 minutes and then OFF between.1 and 4 minutes for 6 hours as the 6 hour device does, however after 6 hours it changes so that the light is ON between 1 and 4 minutes and OFF for between 6 and 37 minutes for the is next three hours or the remainder of the night depending on the type, which reflects the pattern of light switching ON and OFF which one would expect to see if a family or householder had gone to bed but had to make occasional trips to the bathroom.

As is well known for deterrent devices of the type described the adaptor is activated by switching the lamp on, off, and on at the mains in quick succession is common. This is done by the external C-R circuit 142, 144, 146 and 148 linkedto part P0C3 of the microprocessor.

As is known in the art, the deterrent device includes means to periodically check whether it is dark or light outside periodically in case it has been fooled to thinking it is dark by a thunder storm or conversely fooled into thinking it is light by some car head lights shinning in the room. This is done by readings being taken when the lamp is switched OFF at the end of one of its ON periods to determine whether it is light or dark and checking again three minutes later to confirm the result.

is In a particular embodiment, not shown, the microprocessor includes an infra red or radio wave receiver which can be remotely activated to switch the light on by infra red or radio waves, respectively.

Alternatively the light may also be sound activated.

Claims (9)

CLAIMS:

1. A deterrent device comprising an adaptor including a plug means which is connectable to a light bulb socket and a socket means which is arranged to be able to receive a light bulb wherein the adaptor includes means for switching the light bulb on and off said means including a triac connectable in series with the light bulb across an AC mains electricity supply, the gate of the triac being controlled by the microprocessor and wherein in use current is supplied to the gate of the triac for a short period after each zero crossing of the AC current through the triac, the arrangement being such that the average current is supplied to the gate of the triac to drive the triac is less than would be required if the triac were driven continuously.

2. A deterrent device according to claim 3, wherein the a clock which is arranged to time the period between the time when the deterrent device is switched on, off and m at the mains and if that time - 18 is less than a certain short period to switch the deterrent device into its activated mode.

3. A deterrent device of the type described, wherein the microprocessor is arranged to switch the light bulb on and off at random.

4. A deterrent device according to claim 3, wherein the microprocessor includes an internal counter which is switched on when the device is activated and which counts until after the light sensing means determines it is dusk.

5. A deterrent device according to claim 4, is wherein at a particular time after dusk, the values of one or more of the bits of the random number generated by the counter at dusk is used to determine how long the light bulb is switched on for, and the arrangement is such that the counter continues to run and when the light is switched off the number on the counter is used to generate the duration the light bulb is off for.

6. A deterrent device of the type described which when activated is arranged to switch a light bulb on around dusk and then continue to switch the light bulb on and off during a first period wherein on average, the light bulb being arranged to be on for 70-95% of the duration of the first period and off for 5-30% of that period, followed by a second period during which the light is on for 5-30% of the duration of that period and off for 70-95% of the period on average.

7. A deterrent device according to claim 6, wherein the light is on for 85-95%, and off for 5-15%, of the first period and off for 85-95%, and on for 5-15% of the second period.

8. A deterrent device according to claim 6 or claim 7, wherein the first period is between 4 to 8 hours long and the second period is 2 to 4 hours long.

9. A deterrent device ofthe type described which includes infra red or radio receiving means, or sound activatable means, arranged to switch the light bulb on when a suitable signal is received.